I am working with ADO connection with C++ where I connect to DataBase fetch records and close connection. ,
My porblem is we have to connect, fetch records and close connection every time for single user and we have more than one million users.
Is there any way that we can keep connection alive or have some pooling mechanism running background so we done have to connect always ?
I searched for connection pooling with C++ , but could not find anything
Thanks in advance
Connections are pooled by default with ADO classic (which uses OLEDB services for connection pooling). The cost of the physical network connection is incurred only during the initial open. As long as you properly close/dispose connections, the subsequent overhead is minimal without coding to handle persistent connections.
Related
We have lots of micro services which need connection to DB. Oracle and PostgreSQL can handle just limited amount of connections. PostgreSQL solve this situation with PgBouncer so application connect to this URL which handle connection pooling. Is there something similar in Oracle ? What I found is oracle UCP but I think this is still pooling in application not in DB.
If your clients drivers are not too old (pre oracle-12) you can use Oracles Database Resident Connection Pooling.
See https://docs.oracle.com/en/database/oracle/oracle-database/19/jjdbc/database-resident-connection-pooling.html#GUID-D4F9DBD7-7DC6-4233-B831-933809173E39
Database Resident Connection Pooling
Database Resident Connection Pool (DRCP) is a connection pool in the server that is shared across many clients. You should use DRCP in connection pools where the number of active connections is fairly less than the number of open connections.
Especially database administrators will love this because they can have a good control on the hits on the database.
With JDBC, I understand each connection represents a physical tcp connection with database.
But in MyBatis, there is not connections but sessions, so what is the difference between session and connection?
When I open a session or close a session, what happen internal? Is this mean create/close a connection?
First of all, JDBC connection does not represent physical TCP connection. TCP connection basically allows only to do very few operations, the main one to send an array of bytes to the application on the other end of the connection.
JDBC connection uses TCP connection underneath but it is a higher level abstraction that allows the application to do the more high level operation, namely, to execute SQL queries.
Similarly, SQLSession in mybatis uses JDBC connection but is even more high level concept. Mainly, it allows to execute sql query and map the result to object as specified by the mapping.
[using the JavaScript driver]
I've seen on several of the rethinkdb example projects that connections are closed at the end of each query (e.g., conn.close())
While I understand the pedagogical reasons to include that in the tutorials, is it actually performant to manually close connections? I am under the impression that the connection will automatically close once it is out-of-scope
You should not leave connections open..
You should:
1) Open connections as late as possible
2) Close connections as soon as possible
The connection itself is returned to the connection pool. Connections are a limited and relatively expensive resource. Any new connection you establish that has exactly the same connection string will be able to reuse the connection from the pool.
Communicate with the database in java, we often follow these steps:
load a driver
get a connection
create a Statement or PreparedStatement
get the ResultSet
close the connection
I am confused that we should close connection, all say that create a connection is expensive, so why we can't do like this:
static
{
try
{
connection = DriverManager.getConnection(connectorURL,
user, password);
} catch (SQLException e)
{
e.printStackTrace();
}
}
We just create a connection as a singleton, and use it everywhere. Couldn't it? If I use it like this, what will happen?
And if I don't close the connection, what will happen?
Also, we will use a connection pool, it will create some connections in the pool, and we get the connection from the pool, the connection in the pool also don't close, why if we don't use pool, we need follow the steps and close the connection if we don't use?
It's so confused and I don't know the what's the principle. Please help me. Thanks.
If we don't close the connection, it will lead to connection memory leakage. Until application server/web server is shut down, connection will remain active, even if the user logs out.
There are additional reasons. Suppose database server has 10 connections available and 10 clients request for the connection. If the database sever grants all of them, and after their usage they are not closed, the database server would not be able to provide any other connection for another request. For that reason we need to close them - it is mandatory.
Furthermore, it might lead to some mischievous activities regarding the integrity of the database.
We just create a connection as a singleton, and use it everywhere. Couldn't it? If I use it like this, what will happen?
In this case, you will have only a single database connection. If database query is having a longer execution time, then other requests for that connection object will have to wait. So, this is not a recommended approach.
And if I don't close the connection, what will happen?
By closing the connection, objects of Statement and ResultSet will be closed automatically. The close() method is used to close the connection. If you forget to do so, it will lead your app to connection memory leak. For Example: Imagine that your app has 10 database connections and 10 users are active at the same time. Later on, 3 users log out of the app, but because you didn't implement connection closing mechanism, those 3 connections remain active, and as a result, your app will not provide any other connection to some other user. Also, increased number of opened connections, in database server, slows down the app. So, release the Connection object's database and JDBC resources immediately, instead of waiting for them to be automatically released.
Also, we will use a connection pool, it will create some connections in the pool, and we get the connection from the pool, the connection in the pool also don't close, why if we don't use pool, we need follow the steps and close the connection if we don't use?
Connection pooling means that connections are reused rather than created each time a connection is requested.
This source says, that: "If the system provides connection pooling, the lookup returns a connection from the pool if one is available. If the system does not provide connection pooling or if there are no available connections in the pool, the lookup creates a new connection. The application benefits from connection reuse without requiring any code changes. Reused connections from the pool behave the same way as newly created physical connections. The application makes a connection to the database and data access works in the usual way. When the application has finished its work with the connection, the application explicitly closes the connection.
The closing event on a pooled connection signals the pooling module to place the connection back in the connection pool for future reuse."
Your application borrows a connection from the pool, uses it, then returns it to the pool by closing it. A connection in the free pool for a long period of time is not considered an issue.
I'm using NHibernate and ODP.NET to connect to a Oracle 11g database. Of course there can be connection errors (network failure, DB down, ...). I'm handling all these exceptions in my code, so no problem there. But of course the user can retry his actions (maybe it was just a short network failure), and there comes my problem:
ODP.NET is using connection pooling by default. No problem with that usually, but when the user retries an action after a connection error, NHibernate gets an invalid (pooled) connection from ODP.NET. The user has to retry it multiple times (until the pool is empty) to get it working again.
Of course I can disable connection pooling in ODP.NET, but I'd like to avoid that. I've also read about a setting that checks the connection to the DB for each returned connection from the pool, but this adds an additional round trip to each connection which I'd like to avoid too.
Is there any way to configure ODP.NET to automatically clear the connection pool when any connection throws an connection exception?
If you can use odac (odp) 11g, you have setting Validate Connection for your pool. It can validate the connection before you use it.
The Validate Connection attribute validates connections coming out of the pool. This attribute should be used only when absolutely necessary, because it causes a round-trip to the database to validate each connection immediately before it is provided to the application. If invalid connections are uncommon, developers can create their own event handler to retrieve and validate a new connection, rather than using the Validate Connection attribute. This generally provides better performance.
If it will not be good enough - you can try this document from oracle.
Connection Pool Management
ODP.NET connection pool management provides explicit connection pool
control to ODP.NET applications. Applications can explicitly clear
connections in a connection pool.
Using connection pool management, applications can do the following:
Note: These APIs are not supported in a .NET stored procedure. Clear
connections from connection pools using the ClearPool method.
Clear connections in all the connection pools in an application
domain, using the ClearAllPools method.
When connections are cleared from a pool, ODP.NET repopulates the pool
with new connections that have at least the number of connections set
by Min Pool Size in the connection string. New connections do not
necessarily mean the pool will have valid connections. For example, if
the database server is down when ClearPool or ClearAllPools is called,
ODP.NET creates new connections, but these connections are still
invalid because they cannot connect to the database, even if the
database comes up a later time.
It is recommended that ClearPool and ClearAllPools not be called until
the application can create valid connections back to the database.
.NET developers can develop code that continuously checks whether or
not a valid database connection can be created and calls ClearPool or
ClearAllPools once this is true.
Also, may be this post will help you.
Update:
As pointed by #MPelletier, for oracle 12 the link is different.
Generally speaking, you should avoid trying to manipulate the connection pool for any ADO.NET provider (and also WCF channels - an aside). If you application needs to be resilient in the face of underlying data errors (e.g. timeouts, broken connections in pool, etc.) then you should implement the appropriate level of transaction to ensure data integrity and retry logic to re-execute the failed operation.